Coburn_Performance
03-24-2014, 08:18 AM
Hello All,
I'm just trying to get a few things straight in my mind before I go any further in my current project. I've read a ton on this board and from a wide variety of suspension books and would like to know if there is any consensus on what a reasonable start point for suspension movement would be. I've tried talking to some experts, but when they find out I'm not building a race car then I get the brush-off pretty quickly which is frustrating when you're trying to learn and all you have are either racing books or endless academic volumes for passenger cars and nothing much in between :hammer:.
So, I'd like to keep this simple (but not too simple) and see if I can work my way through it...and I learn things by doing them (when they are mechanical) so telling me to read is pretty much useless (I've done that, I get it, but I don't know it because I've not done it...sorry). So I need a little hand-holding I'm afraid. I've never done anything quite this extensive before.
For my rear suspension (Toyota IRS) I'm trying to get some confirmation that around 7" of total wheel travel is sufficient for a street car that will see some track time. 4" of bump and 3" of droop. I really need this number confirmed as I have to get a coil over pronto so that I can properly fabricate the mounts. I've been using a "mock up" coil over and I'm not really comfortable that I'll not have issues with clearance when I'm done.
https://static1.pt-content.com/images/pt/2014/03/Lethbridge2014022700666_zpsebb1a5d7-1.jpg (http://s862.photobucket.com/user/grpA_240/media/Volvo_122_Restoration/Lethbridge-20140227-00666_zpsebb1a5d7.jpg.html)
I have measured and calculated my motion ratio at 0.79, so a 6" stroke shock should give me the travel that I need. I'm not overly concerned with valving or even spring rate (as I don't have an accurate corner weight at the moment - I'm using what was there and the MR and the new spring angle to get in the ball park). I moved the suspension through 4" of travel from 2" bump to 2" droop measuring from the hub suspension mount to a fixed point on the frame every 1/4" of wheel travel and got a perfectly linear motion.
https://static1.pt-content.com/images/pt/2014/03/IMG_20140318_175259_zpsde0a92c0-1.jpg (http://s862.photobucket.com/user/grpA_240/media/Volvo_122_Restoration/IMG_20140318_175259_zpsde0a92c0.jpg.html)
Here's the hub mount point.
https://static1.pt-content.com/images/pt/2014/03/Lethbridge2014022600656_zpsef549d76-1.jpg (http://s862.photobucket.com/user/grpA_240/media/Volvo_122_Restoration/Lethbridge-20140226-00656_zpsef549d76.jpg.html)
Bracket has to go up in the trunk somewhere. New frame notched for clearance at an installed angle of around 25 degrees at ride height.
https://static1.pt-content.com/images/pt/2014/03/Lethbridge2014030100670_zpseac14af4-1.jpg (http://s862.photobucket.com/user/grpA_240/media/Volvo_122_Restoration/Lethbridge-20140301-00670_zpseac14af4.jpg.html)
Subframe with adjustable links.
https://static1.pt-content.com/images/pt/2014/03/Lethbridge2014022200618_zps75c5b01d-1.jpg
(http://s862.photobucket.com/user/grpA_240/media/Volvo_122_Restoration/Lethbridge-20140222-00618_zps75c5b01d.jpg.html)So can someone confirm that this is in the ballpark? What else do I need to consider? What needs to be computed?
I'm just trying to get a few things straight in my mind before I go any further in my current project. I've read a ton on this board and from a wide variety of suspension books and would like to know if there is any consensus on what a reasonable start point for suspension movement would be. I've tried talking to some experts, but when they find out I'm not building a race car then I get the brush-off pretty quickly which is frustrating when you're trying to learn and all you have are either racing books or endless academic volumes for passenger cars and nothing much in between :hammer:.
So, I'd like to keep this simple (but not too simple) and see if I can work my way through it...and I learn things by doing them (when they are mechanical) so telling me to read is pretty much useless (I've done that, I get it, but I don't know it because I've not done it...sorry). So I need a little hand-holding I'm afraid. I've never done anything quite this extensive before.
For my rear suspension (Toyota IRS) I'm trying to get some confirmation that around 7" of total wheel travel is sufficient for a street car that will see some track time. 4" of bump and 3" of droop. I really need this number confirmed as I have to get a coil over pronto so that I can properly fabricate the mounts. I've been using a "mock up" coil over and I'm not really comfortable that I'll not have issues with clearance when I'm done.
https://static1.pt-content.com/images/pt/2014/03/Lethbridge2014022700666_zpsebb1a5d7-1.jpg (http://s862.photobucket.com/user/grpA_240/media/Volvo_122_Restoration/Lethbridge-20140227-00666_zpsebb1a5d7.jpg.html)
I have measured and calculated my motion ratio at 0.79, so a 6" stroke shock should give me the travel that I need. I'm not overly concerned with valving or even spring rate (as I don't have an accurate corner weight at the moment - I'm using what was there and the MR and the new spring angle to get in the ball park). I moved the suspension through 4" of travel from 2" bump to 2" droop measuring from the hub suspension mount to a fixed point on the frame every 1/4" of wheel travel and got a perfectly linear motion.
https://static1.pt-content.com/images/pt/2014/03/IMG_20140318_175259_zpsde0a92c0-1.jpg (http://s862.photobucket.com/user/grpA_240/media/Volvo_122_Restoration/IMG_20140318_175259_zpsde0a92c0.jpg.html)
Here's the hub mount point.
https://static1.pt-content.com/images/pt/2014/03/Lethbridge2014022600656_zpsef549d76-1.jpg (http://s862.photobucket.com/user/grpA_240/media/Volvo_122_Restoration/Lethbridge-20140226-00656_zpsef549d76.jpg.html)
Bracket has to go up in the trunk somewhere. New frame notched for clearance at an installed angle of around 25 degrees at ride height.
https://static1.pt-content.com/images/pt/2014/03/Lethbridge2014030100670_zpseac14af4-1.jpg (http://s862.photobucket.com/user/grpA_240/media/Volvo_122_Restoration/Lethbridge-20140301-00670_zpseac14af4.jpg.html)
Subframe with adjustable links.
https://static1.pt-content.com/images/pt/2014/03/Lethbridge2014022200618_zps75c5b01d-1.jpg
(http://s862.photobucket.com/user/grpA_240/media/Volvo_122_Restoration/Lethbridge-20140222-00618_zps75c5b01d.jpg.html)So can someone confirm that this is in the ballpark? What else do I need to consider? What needs to be computed?